1. Field of the Invention
The present invention relates to a radio selective calling receiver and, more particularly, to a radio selective calling receiver having a function of limiting the frequency of reception of messages.
2. Description of the Related Art
FIG. 1 shows the arrangement of a conventional radio selective calling receiver. The radio selective calling receiver is constituted by a reception antenna 1 for receiving a carrier wave modulated by a call number and a message, a reception circuit 2 for demodulating the signal received by the reception antenna 1, a decoder 3 for determining whether the received signal is for the home receiver, and decoding the signal, an EEPROM 4 for storing the call number of the home receiver, a battery saving control circuit (to be abbreviated to BS control circuit) 5 for controlling power supply to the reception circuit 2, an incoming message memory 7 for storing incoming messages, a switch operation unit 11, a detection circuit 12 for detecting the operation of the switch operation unit 11, an LCD 17 for displaying a message, a display control unit 16 for controlling the display operation of the LCD 17, and a CPU 6.
As shown in FIGS. 2 and 3, after the power switch of the radio selective calling receiver is turned on (step F-1), the BS control circuit 5 performs control (BS operation 1) to intermittently supply power to the reception circuit 2 until a preamble signal for bit synchronization is received. The reception circuit 2 performs an intermittent reception operation (step F-2). When a preamble signal is detected by the decoder 3 (step F-3), the decoder 3 outputs a signal to the BS control circuit 5 to stop the intermittent power supply to the reception circuit 2 and keep it on (step F-4). The reception circuit 2 continues the reception operation and waits for a frame synchronization signal. When the frame synchronization signal is detected (step F-5), the BS control circuit 5 performs control (BS operation 2) again (step F-6) to intermittently supply power to the reception circuit 2 so as to allow the reception circuit 2 to operate at a timing matched with a frame number corresponding to the call number of the receiver and wait for the call number of the home receiver. When the call number of the home receiver is detected by the decoder 3 (step F-7), power is intermittently supplied to the reception circuit 2 (step F-8). A message for the home receiver, which is received after the call number, is then decoded (step F-9) and stored in the incoming message memory 7. If an incoming signal is continuously received (step F-11) after all messages are received (step F-10), a call number is waited for (step F-7). If no incoming signal is received, the flow returns to the step of waiting for a preamble signal (step F-3). The intermittent power supply operation (BS operation 1) is then performed (step F-4).
In this conventional radio selective calling receiver, when information corresponding to a designated call number is transmitted on a radio signal to the receiver, a message added to the call number is received. For this reason, all the messages transmitted from the transmission side, including information unnecessary for a user on the reception side, must be received.
Essentially, a conventional radio selective calling receiver of this type is a means for transmitting messages to each user on the reception side. Therefore, all the messages which are transmitted to the receiver under its selective call number peculiar to the receiver are to be received. Among recently developed radio selective calling receivers, there is one capable of enjoying a so-called simulcast service under which one radio selective calling receiver has a plurality of selective call numbers, one being peculiar to the receiver and the others being common to some other receivers and the one receiver is capable of receiving either a call and a message peculiar to itself under the peculiar call number or a call and a message common to the other receivers under the common call number. The simulcast service allows transmission of the same message to a plurality of radio selective calling receivers. That is, simultaneous transmission can be performed. Some of the messages received under the simulcalst service may be unnecessary for a user on the reception side, but the user on the reception side cannot select incoming messages.
As described above, the conventional radio selective calling receiver does not allow a user on the reception side to select incoming messages. Therefore, with an increase in the number of messages transmitted, the reception circuit of the receiver has to operate unnecessarily more frequently, resulting in an increase in the power consumption of the receiver.